Question

How many grams of oxygen gas are needed to produce 36.0 grams of water ?

Answer 1

32 grams.

Explanation:

The best way is to look at the reaction between Oxygen and Hydrogen, and then balance it:

`2H_2 +O_2 -> 2H_2O`

From this we can see the molar ratios.

Now, 36 grams of water equals two moles of water from the equation:

`n=(m)/(M)`
`m=36 g`
`M=18 gmol^-1)`
Hence
`n= 2` (moles)

Thus according to the molar ratio, we should have half the amount of moles, that is one mole of diatmoic oxygen. 1 Oxygen atom has a mass of 16 grams, thus diatomic oxygen weights twice as much- 32 grams.

Hence 32 grams is needed.